EFFECTS OF NATURAL, SYNTHETIC, AROMATIZABLE, AND NONAROMATIZABLE ANDROGENS IN INDUCING MALE SEX-DIFFERENTIATION IN GENOTYPIC FEMALE CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA)

The relative potency of several androgens to induce the male phenotype in sexually undifferentiated genotypic female chinook salmon were compared in two separate experiments. The aromatizable and nonaromatizable androgens testosterone (T) and 11-ketotestosterone (11-KT), and the synthetic aromatizable and nonaromatizable androgens 17α-methyltestosterone (MT) and 17α-methyldihydrotestosterone (MDHT) were administered to newly hatched alevins in a single 2-hr immersion treatment at doses ranging from 3.2 μg/liter to 10 mg/liter. The influence of these treatments on sex differentiation was evaluated by the histological examination of the resulting gonads 6 and 11 months later. In the control group, which was not exposed to exogenous steroids, no males or intersex fish were observed. In contrast, essentially 100% masculinization occurred in groups exposed to MDHT at dosages of 400 μg/liter and higher. Treatment with the aromatizable androgen MT resulted in a dose-dependent masculinization, with the production of 100% males at 400 μg/liter. However, higher doses resulted in fewer males. 11-KT and T were less potent than the synthetic androgens. The number of males produced after treatment with 11-KT followed a dose-dependent pattern while T showed virtually no masculinizing effect in inducing male phenotype in these studies. The resultant AD50 dosage levels (dosage at which 50% of the genotypic females were sex-reversed into phenotypic males) after a single 2-hr immersion treatment were: 30, 60, and 500 μg/liter for MDHT, MT, and 11-KT, respectively. Thus, in addition to quantifying the relative masculinizing potencies of these androgens in this sensitive model, these experiments suggest that the susceptibility of an androgen to aromatization may influence its relative masculinizing potency, and that 11- KT rather than T may be involved in the process of sex differentiation in this species. © 1993 by Academic Press, Inc.